Convert CONFIG_SYS_BR0_PRELIM et al to Kconfig

This converts the following to Kconfig:
   CONFIG_SYS_BR0_PRELIM
   CONFIG_SYS_OR1_PRELIM
   CONFIG_SYS_BR1_PRELIM
   CONFIG_SYS_OR2_PRELIM
   CONFIG_SYS_BR2_PRELIM
   CONFIG_SYS_OR2_PRELIM
   CONFIG_SYS_BR3_PRELIM
   CONFIG_SYS_OR3_PRELIM
   CONFIG_SYS_BR4_PRELIM
   CONFIG_SYS_OR4_PRELIM
   CONFIG_SYS_BR5_PRELIM
   CONFIG_SYS_OR5_PRELIM
   CONFIG_SYS_BR6_PRELIM
   CONFIG_SYS_OR6_PRELIM
   CONFIG_SYS_BR7_PRELIM
   CONFIG_SYS_OR7_PRELIM

This also introduces CONFIG_SYS_BR0_PRELIM_BOOL as not all platforms
that can set these values do so.  Add the relevant SYS_BRx_PRELIM_BOOL
to platforms that had not been previously migrated.

Signed-off-by: Tom Rini <trini@konsulko.com>